An animal's immune system is comprised of numerous elements that act separately and/or in concert to counteract, to eliminate, or to neutralize substances that are recognized by that system as foreign to the animal host. Generally, but not necessarily, the substance recognized as foreign by the immune system has its origin exogenous to the host. Exemplary of such exogenous substances are infectious bacteria and the by-products of their cellular activity, virus particles and their proteins, proteins injected by insect stings, and the like. In autoimmune diseases, such as rheumatoid arthritis, the host's immune system recognizes host-made proteins or self-made proteins as foreign.
The principal effectors of the immune system are the leukocytes, which include lymphocytes of thymic origin (T cells), lymphocytes produced in bone marrow (B cells), neutrophils which, inter alia, produce enzymes that make oxidizing agents such as hydrogen peroxide that have cytotoxic effects upon bacteria, and macrophages which present the foreign substance or antigen to the T cells, as well as produce a protein designated interleukin-1 that assists T cell transformation into T helper cells. Complement which is a complex mixture of proteins that acts in an ordered, cascading manner upon the foreign substance also plays a major role in immune responses.
B cells can be distinguished from T cells, inter alia, by the presence of immunoglobulins on their membrane surfaces. The membrane-bound immunoglobulins function as antigen receptors; secreted immunoglobulins function as antibodies.
There are five known classes of immunoglobulins, identified as IgA, IgD, IgE, IgG, and IgM on the basis of five antigenically different heavy chain proteins which in part make up the immunoglobulin molecule. B cells also bear non-immunoglobulin cell markers, including a complement receptor (CR), a receptor for the Fc portion of immunoglobulin (FcR), I-region associated antigens (Ia), and a set of differentiation antigens (Lyb 1-7) which are identified by all antisera and are correlated with various aspects of B cell maturation and activation. These markers are useful in phenotypically identifying B cells.
While the B cell immunoglobulins interact with the foreign substance, or antigen, the T cells, and particularly helper T cells, are believed necessary to stimulate B cells to divide and to differentiate into antibody secreting cells for humoral immunity. Suppressor T cells contribute to the regulation of humoral immunity, while cytotoxic T cells and T cell mediators of delayed-type hypersensitivity are the principal effectors of cell mediated immunity.
T cells bear antigens designated Lyt 1, 2, and 3 as well as L3T4 that are related to T cell functions. Helper T cell precursors are of the Lyt 1.sup.+, 2.sup.-, 3.sup.-, L3T4.sup.+ phenotype. It is these cells which normally participate in the activation and regulation of B cells.
Helper T cells are known to assist in activation and differentiation of immunoglobulin-secreting B cells after a first message is received by the B cells from the activating antigenic agent. However, the mode by which the T cells provide the second message of activation and differentiation to the B cells is not entirely understood currently.
Guanosine-3',5'-cyclic monophosphate (cGMP) has been implicated as a naturally occurring agent for providing the required second message for B cell proliferation. 8-Bromoguanosine-3',5'-cyclic monophosphate (8-BrcGMP) has been found to be a weak synthetic intracellular lymphocyte mitogen.
The immune response can be modified by artificial supression (immunosuppression) or enhancement (immunopotentiation or immunostimulation). Immunosuppression; i.e., artifically induced decreased responsiveness, can be achieved by six general methods: (1) blockade by antigen, (2) administration of specific antisera or antibody, (3) use of other biologic reagents such as antilymphocyte antisera, (4) use of drugs or hormones, (5) radiation, and (6) surgical removal of lymphoid tissue. Immunopotentiation can include the administration of an agent effecting an increase in the rate at which the immune response develops, an increase in the intensity or level of the response, a prolongation of the response, or the development of a response to an otherwise non-immunogenic substance.
The agents that are known to enhance immune responses are generally termed adjuvants and can be placed into two general classes: (1) those providing general potentiation; i.e., substances that enhance cellular and/or humoral immune responses for a wide variety of antigens, and (2) those providing specific potentiation, i.e., substances which enhance specific responses to certain antigens only.
Substances that can act as class-1 adjuvants can be grouped into the following categories: (1) water and oil emulsions, e.g., Freund's adjuvant, (2) synthetic polynucleotides, (3) hormones, drugs and cyclic nucleotides, (4) endotoxins, (5) proteinaceous lymphokines and monokines, e.g., interleukins.
An immunopotentiated state can be illustrated by the bodily condition after vaccination. Here, the immune response is already enhanced due to an antigenic response, but could be beneficially enhanced still further to provide an improved degree and/or duration of immunity.
Immunopotentiation can occur in animals that exhibit a normal immune response as well as in animals that exhibit a compromised immune response. In the latter situation, immunopotentiation is relative to the immunocompromised status of the host animal, and rather than enhancing the response to supernormal levels, a protective degree of immunity (i.e., nearly normal levels) is sought and is referred to as immuno-reconstitution. References to immunoenhancements hereinafter are to be understood to include immuno-reconstitution.
In some diseases and physiological conditions such as AIDS, X-linked agammaglobulinemias, senescence and drug-induced-immunosuppression, antigen-dependent B cell activation and differentiation is lacking and/or exists only at a reduced level, thereby lessening the humoral immune response of the host. These diseases and conditions are representative of immunosuppressed states. Here, enhanced activation and differentiation, if it can be effected, tends to beneficially lessen the disease manifestation and/or improve the patient's condition.
Co-assigned U.S. Pat. No. 4,539,205 to Goodman and Weigle describes modulation of animal cellular responses with 8-substituted guanine derivatives bonded 9-1' to an aldose having 5 or 6 carbon atoms in the aldose chain (ring). The cellular modulations described in that patent relate mostly to immunomodulation such as adjuvanticity in enhancing primary and secondary immune responses. Activity against certain neoplastic conditions is also disclosed as are T cell-replacing activity, an IL-1 like activity (assayed on thymocytes), and induction of the release of lysosomal enzymes from neutrophils. The 8-substituents in those molecules have electron withdrawing inductive effects relative to hydrogen. Thus, halo, mercapto or its thioxo tautomer, acyl mercapto, alkyl sulfido, nitro, cyano, keto, halomethyl and methyleneoxy alkyl and the like were disclosed as useful, while electron donating substituents such as an amino group were found to be inactive.
In addition, co-assigned U.S. Pat. No. 4,643,992 and its corresponding published European patent application No. 83306791.1 further disclose the use of derivatives of 8-hydroxyguanosine (8-oxoguanosine), 7-methyl-8-oxoguanosine and 7-methyl-8-thioxoguanosine in modulating animal cellular responses. Further results using guanine derivatives disclosed in U.S. Pat. No. 4,539,205 are also disclosed in U.S. Pat. No. 4,643,992, as are similar results using guanine derivatives disclosed for the first time in that patent.
Still further, several papers and book chapters have been published by some of the present inventors and their co-workers relating to still further effects of compounds disclosed and claimed in U.S. Pat. No. 4,643,992. Exemplary of those published papers are Goodman, Proc. Soc. Exp. Biol. Med., 179:479 (1985); Goodman, J. Immunol., 136:3335 (1986); Goodman and Weigle in Purine Metabolism In Man, Part B, Nyhan and Thompson, eds., Plenum Press, New York, page 451 and 443 (1986); Goodman and Weigle, J. Immunol., 135:3284 (1985); Goodman and Wolfert, Immunol. Res., 5:71 (1986); Goodman, J. Immunol., 137:3753 (1986); and Goodman and Hennen, Cell. Immunol., 102:395 (1986).